The Lives of the Twelve Caesars is a set of biographies of the rulers of Rome from Julius Caesar through Domitian: Caesar, Augustus, Tiberius, Caligula, Claudius, Nero, Galba, Otho, Vitellius, Vespasian, Titus, and Domitian. Suetonius served as an imperial secretary with access to archives, and he writes as a biographer rather than a historian, more interested in the men than in the causes of events.
Each life tends to follow a recognizable pattern. Suetonius opens with family and ancestry, moves through the subject's rise and public acts, then turns inward to describe the person: appearance, dress, health, tastes, habits, and superstitions. He records the ruler's virtues and his vices side by side, often with a deliberate pivot from the prince to the private appetites once power removes restraint.
The method is anecdotal and impartial in tone. Suetonius relates rather than argues. He sets down sayings, table talk, scandals, acts of generosity, and acts of cruelty, frequently flagging conflicting reports with phrases such as some say or it is said. He paints little and explains less, leaving the reader to assemble a judgment from the mass of particulars.
Omens and prodigies run through the book. Births are attended by portents, victories foretold by signs, and deaths preceded by warnings the ruler ignores or misreads. Suetonius treats these not as decoration but as part of how a Roman life was understood, binding fortune, character, and fate together in the same record.
Read as a whole, the work is a study of what power does to character. The early Caesars build and consolidate an empire; later figures squander it in luxury, fear, and blood; brief usurpers rise and fall in a single turbulent year. The famous deathbed lines Suetonius preserves distill each man in a sentence, and the cumulative effect is a gallery of rulers measured less by policy than by the kind of human being each became.